Food products, particularly liquid or pasty products, in contact with ambient air are subjected to numerous risks of biochemical or microbiological alterations which include darkenings, loss of flavor, loss of vitamins, and development of disagreeble tastes.
The risks of degradation of these products, correctly controlled during production, remain very great during storage after packaging. To reduce degradation and to increase the period of preservation, it is essential to reduce the oxygen content of the gas volume of the packages: on empty packages to limit the reoxygenation of the product during filling and/or on filled packages to avoid the presence of gaseous oxygen on the surface of the product.
There are numerous techniques and equipment making it possible to reduce the gaseous oxygen content of airtight packages of liquid, pasty or solid products passing on a packaging line.
Subjecting the contents and the package to a vacuum, with or without gaseous compensation, is very effective for packaging solid products; it becomes difficult to use on liquid or pasty products because the value of the vacuum used remains limited by the risks of aspiration of the product. This technique cannot be used for high packaging rates, it uses expensive equipment, and it is difficult to integrate in a packaging line of liquid or pasty products.
Simple gas sweeping has been proposed. In this method, the oxygen is purged by an injection of inert gas; residual contents of gaseous oxygen of less than 2% are difficult to achieve, the purge being performed in ambient air atmosphere.
According to another technique, desorption of dissolved gas is used, and the gaseous medium of the packages can be rendered inert by purging the oxygen with an inert gas previously dissolved in the liquid. This is the case, for example, of carbonated beverages such as beer where the desorption of the CO.sub.2, obtained by injection of hot water on the surface of the liquid, causes a foaming and an inerting of the gaseous medium of the package. The drawback of this technique is that a foam is created that can impede closing of the package and cause considerable losses of the liquid (an average of 1 to 2%).
Further, the oxygen content of airtight packages of food products can be reduced by injection of a cryogenic fluid. According to this technique, after injection of the cryogenic fluid--essentially nitrogen or carbon dioxide--inerting of the package is obtained by vaporation of the fluid and purging of the oxygen by the generated inert gas. The efficiency of inerting of such systems on high-rate packaging lines remains imperfect, the average contents of residual oxygen of the packages being very variable and, on the average, greater than 2%.
To avoid degradation of certain food products, particularly liquids and pastes, it is essential to lower the oxygen content of the air in contact with these products to values below 2%.
Within the context of preserving food products, inerting equipment was sought that would be easy to adapt to a packaging line, making it possible to assure filling of the packages and/or storage of the packaged product in a gaseous medium at less than 2% oxygen.